How the four vendors compare

We score three things on every vendor: whether an outside lab wrote the purity report, whether that report names the batch you would receive, and whether the testing method is stated. Each check is a pass, a partial, or a fail, worth 2, 1 or 0 points, for a documentation score out of 6. The full method is on the homepage, and the checks themselves are explained in our guides on reading a certificate of analysis and HPLC and mass spectrometry.

1. Peptryn (6/6)

Complete public paperwork for the products we checked.

Outside lab

Pass

Batch-matched

Pass

Method stated

Pass

Purity on file

99.6 to 99.97%

Affiliate program

20% commission per referred sale

Read the full Peptryn review

2. American Peptides (5/6)

A public COA library with named lab, lots and methods; unclear which lot ships, and we could not check the lab's verification page.

Outside lab

Pass

Batch-matched

Partial

Method stated

Pass

Purity on file

99.55 to 99.83%

Affiliate program

10% to start, up to 35% with monthly sales

Read the full American Peptides review

3. Core Power Peptides (4/6)

The catalog and price we recommend; the paperwork still has real gaps.

Outside lab

Partial

Batch-matched

Partial

Method stated

Pass

Purity on file

99% (sample COA)

Affiliate program

25% commission per referred sale

Read the full Core Power Peptides review

4. Peptides for Sale (1/6)

Purity and testing claims with no documents.

Outside lab

Fail

Batch-matched

Fail

Method stated

Partial

Purity on file

Claims 99%+

Affiliate program

No program found

Read the full Peptides for Sale review

What this comparison does and doesn't tell you

Peptryn publishes the most documentation of the four we've checked: a public certificate library, a named testing lab, and a batch lookup. American Peptides is close behind, with a public library of 74 current certificates that name the lab, the lot and the methods; it loses a point because we could not tell which lot a given order receives, and because the lab's verification page refused our request. Core Power Peptides shows one sample certificate and states testing happens, but doesn't publish enough for us to check that claim against most of what it sells. Peptides for Sale currently publishes no certificate of any kind.

Core Power Peptides also pays the highest fixed affiliate commission of the four, 25% against Peptryn's 20%. American Peptides starts partners at 10% and rises to 35% with monthly sales, and we are a partner of both it and Core Power Peptides. We flag that because it's the kind of fact that could bias a ranking if we let it; it hasn't moved Core Power above a vendor that documents more. A higher payout is not evidence of better documentation, and we don't treat it as any.

It's also why we're direct about the fact that our featured recommendation, on the homepage and throughout this site, is Core Power Peptides — even though it is third on this table. We made that call on catalog size and pricing. That's a commercial and practical decision, not a documentation one, and the two shouldn't be confused. If published paperwork is what matters most to you, this table says Peptryn is where to look first — and if retatrutide itself, not the dual-agonist tirzepatide we feature, is what you're researching, Peptryn is also one of two of the four that stock it, with two batch-matched certificates; American Peptides lists it too. We got that wrong in an earlier version of this page, which said no vendor we'd reviewed carried retatrutide; that was our error, not a change on Peptryn's end.

None of this tells you whether a peptide is safe to use, because that isn't what a certificate of analysis measures and it isn't a question this site answers. See our guide on what research-use-only labeling does and doesn't mean for what these products are, and aren't, sold to do.